I own both. Both are awesome rba tank systems.
The Aqua is a native dual coil rba. with both juice control and air control. It's basically best suited for sub ohm vaping. I have a vertical mounted 0.3 ohm build on mine. The Aqua is a meticulous rba to build properly. but is fairly easy to do once one has worked out how. I would NOT recommend it to a first time vaper because of this, also having juice control adds an extra level of consideration and learning.
The Russian has a larger tank capacity, and vapes quit well from 8-30 watts. Has great flavor, good solid vape, and fairly easy to build. I good choice for a first timer or an experienced vaper.
All atomizers have different characteristics, subtleties, pros and cons. These two are similar but not even close to the same. So which is better, the one that has juice in it and don't have to refill. lmao.
Get one, then get the other later, or get both, depending on your current gear.